The invention relates to a spring for compression and tension, mainly in axial direction, which spring is made of a material having a Young's modulus of elasticity E, which is at least 39 GPa, such as metal, steel, glass, plastic or reinforced plastic, the spring being rotation symmetrical around a symmetry axis and in the form of a tube or a ring, the material thickness of the spring wall between the end sections of the spring being practically constant. The spring, in its length direction, comprises at least two mutually integrated spring parts, in radial direction oppositely directed, and in cross section half-wave or U-shaped.
A U-shaped spring is known from German published patent application DE-AS 35 36 661, where FIG. 10 shows a rotation symmetrical U-shaped spring, where the wall of the spring has a practically constant thickness of material. The axial ends of this spring loosely abut a cylindrical ring, and consequently there must be radial exterior or interior guiding surfaces to keep the spring in position. Such an interior or exterior guiding surface gives a friction, when the spring moves, and consequently a certain hysteresis loop.
Known are also springs shaped like bellows, which tightfitting confine a temperature expanding medium or a movement suppressing medium, and a common purpose for these types of springs are to obtain a flexibility as large as possible with a spring resistance as small as possible, since the compressive force mainly has to be generated by the medium confined in the spring.